Extensive research has shown that second language (L2) learners find it difficult to apply grammatical knowledge during real-time processing, especially when differences exist between the first (L1) and L2. The current study examines the extent to which British English-speaking learners of French can apply their grammatical knowledge of the French subjunctive during real-time processing, and whether this ability is modulated by the properties of the L1 grammar, and/or proficiency. Data from an acceptability judgment task and an eye-tracking during reading experiment revealed that L2 learners had knowledge of the subjunctive, but were unable to apply this knowledge when reading for comprehension. Such findings therefore suggest that L2 knowledge of the subjunctive, at least at the proficiency levels tested in this study, is largely metalinguistic (explicit) in nature and that reduced lexical access and/or limited computational resources (e.g., working memory) prevented learners from fully utilising their grammatical representations during real-time processing.